Can I get a used car inspected before buying it from a dealership?

Q. I often read that, prior to purchasing a used vehicle, one should have their own mechanic check it over. How is this accomplished when dealing with a dealership? When considering a used vehicle offered for sale by a dealership, in my case a Honda dealership, I can’t see the dealership allowing me to drive the vehicle to my mechanic’s shop since I don’t own it yet. Nor can I see the salesperson taking time out of the day to bring the car to my mechanic’s shop. Should I expect my mechanic to go to the dealership and inspect the car there? I never quite understood how to have a vehicle checked by my own mechanic before purchasing it, especially when buying from a dealership rather than a private seller.

A. For more than 20 years, I ran the AAA Auto Diagnostic Center, and we performed pre-purchase inspections every day. Sometimes the dealer would send the car, while other times the buyer would bring it, either alone or accompanied by the salesperson. These inspections involved everything from 20-year-old vehicles to cars that were only a few months old. It has been my experience that if a dealer is unwilling to allow an independent inspection, it can be a red flag. The conversation generally goes something like this: “I will leave a deposit, usually by credit card, but I want the car inspected first. If the vehicle needs too much work, or if you are unwilling to perform the necessary repairs, the deal is off and my deposit is refunded.” At our shop, a pre-purchase inspection typically took about 90 minutes, including reviewing the results with the buyer and, in some cases, the seller. Some dealers, as well as private sellers, would even have the inspection performed before finding a buyer as a way to help sell the vehicle.

Q. I bought a 2015 Dodge Caravan that keeps setting a P0420 trouble code. The used-car dealer replaced all of the oxygen sensors, then both catalytic converters, and later replaced all four sensors again. The dealer also said all six spark plugs were replaced, but the ignition coils still look dirty and don’t appear to have been handled. The dirt on the intake manifold also doesn’t appear to have been disturbed. I checked the coils on Bank 1, and each one reads between 4,000 and 8,000 ohms. The van runs well and gets about 20 mpg around town and 30 mpg at 60 mph on the highway. Can you suggest anything that may have been missed that keeps causing the check engine light to come on? Is there a scan tool that might help?

A. My first thought is the quality of the replacement parts. I have seen many aftermarket catalytic converters and oxygen sensors that simply do not perform as well as original equipment parts. I would also be looking closely for any exhaust leaks. If I were diagnosing this van, I would start by reviewing the oxygen sensor voltage readings. As a general rule, the upstream oxygen sensor should switch rapidly, while the downstream sensor should remain relatively steady. If the rear sensor mirrors the activity of the front sensor, the catalytic converter is not doing its job. A professional scan tool that can display fuel-trim data, Mode 06 information, and pending misfire codes would be very helpful. Mode 06 allows technicians to view the results of the vehicle’s onboard emissions-system self-tests and can help identify a marginal catalyst, oxygen sensor, or misfire, before a conventional trouble code is set. It is also worth verifying that all six spark plugs were actually replaced, since the rear-bank plugs require additional labor to access. A marginal misfire, exhaust leak, or poor-quality replacement converter can all trigger a recurring P0420 code even when the vehicle seems to run normally.

Q. I have read on Facebook and YouTube that the government will be installing kill switches in cars starting in 2027. From what I have read, manufacturers or the government will be able to shut off cars at will. Is this true or science fiction? I need a new car and usually wait until the new models come out. Should I buy a 2026 model? I don’t want someone else to control my car.

A. I have read those reports as well. Consumer Reports recently published an article on the subject. The confusion stems from the HALT Drunk Driving Act, which was signed into law in 2021. The law directs federal regulators to develop standards for passive impaired-driver detection technology that could prevent or limit vehicle operation if impairment is detected. Published reports show every day, about 32 people in the United States die in drunk-driving crashes — that’s one person every 44 minutes, so you decide.  However, as of 2026, the National Highway Traffic Safety Administration (NHTSA) has not issued a final rule and has told Congress that no commercially available system currently meets the requirements of the law. Interestingly years ago, Saab Automobiles had an experimental prototype concept featuring a miniature breathalyzer (Alcokey) built into the car key fob to prevent drunk driving. According to Consumer Reports, 2027 model-year vehicles are not expected to have any federally mandated technology that determines whether a driver is intoxicated, nor is there any such thing as a government-controlled “kill switch.” The real story is much less dramatic than social media would suggest. Someday future vehicles  could include some form of impaired-driver detection (alcohol and other drugs) technology, but I don’t believe the government will be able to remotely shut down your vehicle at will.

John Paul is AAA Northeast’s Car Doctor. He has over 40 years of experience in the automotive business and is an ASE-certified master technician. E-mail your Car Doctor question to [email protected]. Listen to the Car Doctor Podcast on Apple Podcasts or other popular podcast sites.